Typically, an integrated circuit includes electronic components, such as transistors, capacitors, or the like, integrated into a thin wafer/substrate of semiconductor material, e.g. silicon. Additional materials are deposited and patterned to form interconnections between the electronic components.
During the fabrication process, it may be necessary or desirable to perform one or more planarization processes on the wafer/substrate in order to achieve an atomically-smooth and damage-free surface at feature level. A commonly accepted process to achieve the flat surface involves Chemical Mechanical Polishing/Planarization (CMP). CMP is a process for material removal that uses chemical and mechanical mechanisms to produce a planar mirror-like wafer surface for subsequent processing. This process typically requires that the wafer/substrate be mounted on a carrier or polishing head of a CMP apparatus. The exposed surface of the substrate is placed against a rotating polishing disk pad or belt pad covered at least partially by slurry. A polishing slurry, including at least one chemically-reactive agent and abrasive particles if a standard pad is used, is supplied to the surface of the polishing pad. Both continual slurry movement and constant abrasion by the disk pad of the apparatus lead to a polished wafer surface. The carrier head provides a nominally uniform controllable load on the wafer/substrate to push it against the polishing pad. The carrier head has a retainer ring which holds the substrate in place during polishing.